Development of flocculation models for improving water treatment

In water treatment the flocculation of particles into larger aggregates or ‘flocs’ allows impurities or solid material to be removed more easily by sedimentation.

One example is where soluble phosphorus is removed by dosing with ferric sulphate to form a precipitate containing the phosphorus. Dosing usually requires rapid mixing of the ferric sulphate followed by gentle mixing to encourage flocculation.

The use of Computational Fluid Dynamics (CFD) allows multiphase systems to be modelled and the effect of design changes to be studied in order to optimise water treatment. The development of a framework for modelling flocculation provides the possibility to optimise water treatment processes involving the flocculation of particulates.

The paper describes in greater detail the physical models and verification and validation cases undertaken in order to develop the framework and a case study in which CFD was used to optimise the mixing performance of a flocculation tank.